The invention relates to a (preferably hydraulic) master cylinder for an actuating device of a clutch or a brake of a motor vehicle, such as a car, truck, bus, or agricultural utility vehicle, comprising a cylinder housing having a pressure cylinder section, as well as a piston movably provided in reference to the cylinder housing, with the piston being arranged in the actuated state within the pressure cylinder section in order by a piston to control a fluid pressure in a pressure chamber, fluidically sealed via a sealing device, and being arranged in a pressureless state such that the pressure cylinder section is fluidically connected to a retention system.
Generic master cylinders as well as actuating devices are known from prior art in various embodiments, with for example DE 10 2013 204 561 A1 disclosing a sealing arrangement, particularly a piston cylinder unit. The sealing arrangement comprises an annular seal with a static sealing lip and a dynamic sealing lip, which are connected to each other, with the seal being provided in a seat which has at least one circumferential wall and at least one axial wall. The seal rests here with the static sealing lip radially at the circumferential wall, with the dynamic sealing lip contacting another wall abutting the seat, being dynamically supported. The additional wall has in an axial section a plurality of axial grooves, provided distributed in the circumferential direction, and the dynamic sealing lip has in an axial section of its extension a plurality of axial grooves, provided distributed in the circumferential direction. The axial grooves of the dynamic sealing lip are connected to each other via a circumferential groove.
However it has been shown in these embodiments known from prior art that in case of an extended contact of the respective sealing lip/seal in the groove area, for example in a parking position in which the seal is located in a shut-off state of the master cylinder, disadvantageously a lasting deformation of the sealing lip can occur due to the environmental circumstances; because when the sealing lip, for example in a parking position, at relatively low ambient temperatures abuts an uneven area over an extended period of time, here a deformation of the sealing contour can occur at the seal. When the master cylinder is actuated anew the cold sealing lips can then remain deformed, at least partially and over a first period of time, resulting in the master cylinder exhibiting strong leakage. A reliable function of the master cylinder is then no longer ensured under such circumstances.
It is further disadvantageous in the embodiments known from prior art that the seals/sealing devices require a relatively expensive assembly. Here, particularly when inserting the piston into the cylinder housing, the seals may be subjected to excessive mechanic stress, which can even lead to an abrasion of material at the seals. This would lead to a defect of the respective seat.